1. Field of the Invention
The present invention relates to a force transducer, medical instrument, and machine implemented method.
2. Description of the Prior Art
Diabetes mellitus is a chronic illness with a prevalence approaching 8% in most developed countries. Throughout Europe, there are approximately 27 million registered diabetic individuals; the majority (greater than 80%) of these individuals are presenting Type 2 diabetes. From a UK perspective, the King's Fund has estimated the economic implications of diabetes to reside at £2 billion annually. Moreover, the management of diabetes and its associated complications are set to demand 10% of the total National Health Service (NHS) budget by 2011.
Diabetic peripheral neuropathy is a frequent complication of diabetes mellitus. Its prevalence has been observed to vary between studies, but around 60% of all Type 2 diabetic individuals will eventually develop this condition within the first 10 years of being diagnosed with diabetes. The condition tends to follow a distal to proximal pattern of distribution through the body; hence the toes are often the first areas to exhibit neurological impairment. As such, peripheral sensory neuropathy is regarded as a key factor for the development of ulceration in the diabetic foot.
Research has maintained that an inability to detect a 10 g-force (i.e. 98 mN) applied at key weight bearing sites is a sufficiently capable measurement for neuropathy and, thereby, is consistent with an increased risk of plantar ulceration.
FIG. 1 shows a schematic view of a prior art monofilament testing device 101 for testing for the presence of diabetic peripheral neuropathy in patients. A monofilament 103 is formed of extruded homopolymer, typically polyamide, retained within or fixed to a handle 102. The extruded homopolymer monofilament 103 is fixed at one end (i.e. at the handle 102), allowing for it to be deflected when an axial force is applied to the opposite end. The extruded homopolymer monofilament is used to impart a prescribed force, which is defined by a specified lateral deflection, or buckling, under the associated load.
FIG. 2 shows the monofilament device 102 with an applied axial 10 g-force (i.e. 98 mN) 105, resulting in lateral deflection of the monofilament 104 by bending of 10 mm. The test is typically conducted discreetly, whereby clinicians are required to apply the monofilament at 90° to the target site (one of the key weight points) and observe a 10 mm deflection, thereby applying a 10 g-force (i.e. 98 mN) and noting any patient response.
However, given the apparent variability in fibre length and diameter of the monofilament, in addition to the differences in crystalline structure between grades of polyamide and above all, the material's susceptibility to changes in humidity (hydroscopic changes), the nominal mechanical properties are rapidly compromised during use.
FIG. 3 shows a plot of the mean buckling force fB in gram-force (i.e. units of 9.8 mN) against the number of compressions N of four commercially available ‘10 g-force load’ monofilaments from the vendors: Bailey, Mumford, North Coast and Timesco. The illustrated test results show that all of these devices show a reduction in the force needed to achieve the 10 mm lateral deflection each time the device is used, with significant changes occurring over the course of 10 uses.